In high volume printing applications, laser printers such as the IBM.RTM. 3800.TM. and 3900.TM. series, as well as the Siemens.RTM. 2140.TM., 2200.TM., and 2240.TM. series, lay down images on a continuous web by directing the web through an image element, that, typically, comprises a moving image drum having toner deposited thereon. A portion of such a web 12 is illustrated in FIG. 1. The feeding of the web 12 to the image drum is facilitated by one or more "tractor pin" feed units that engage evenly spaced holes 14 disposed along opposing widthwise edges of the web on "pin feed" strips 16. The widthwise edges having "tractor pin feed holes" therein, as well as the sheets themselves often include perforations 17, 18, respectively, for easy removal.
A typical pin feed application is depicted in FIG. 2. A source 20 of continuous web 22 is driven (arrow 24) to an image transfer element 26 of a printer 28. Toner 30 is provided to the image transfer element or drum 26 by operation of the optical print head 32. A separate developer 34 is provided to attract the toner to the drum 26. The web 24 engages the image drum 26 at a transfer station 36 where printing is laid upon the web as it passes over the image drum 26. The image drum rotates (arrow 38) at a speed matched to the speed of web travel. The web 24 is driven to and from the image drum 26 by a pair of tractor units 40 and 42 that each include a plurality of pins 44 on moving endless tractor beds 45 for engaging pin holes in the edges of the web. The pin holes 14 are detailed in FIG. 1 discussed above.
Downstream of the tractor feed units 40 and 42, the web 24 is directed over a fuser 46 and a preheat unit 48 that fixes the toner to the web 24. The web is subsequently directed to a puller unit 50 that comprises a pair of pinch rollers and into a director chute 52 onto a stack of zigzag folded finished web 54.
A significant disadvantage of a printer arrangement according to FIG. 2 is that the additional inch to inch and one half of web that must be utilized to provide the tractor feed hole strips entails significant waste. The web area between the tractor feed pin hole strips already comprises a full size page and, thus, the tractor feed strips represent area having no useful function other than to facilitate driving of the web into the printer. In a typical implementation, the pin holes are subsequently torn or cut off and disposed of following the printing process.
A variety of utilization devices currently employ tractor pin feed continuous web. Such a feed arrangement is a standard feature on most devices that utilize more than 80 pages per minutes. Specialized equipment has been developed to automatically remove tractor pin feed strips when they are no longer needed. Hence, substantial cost and time is devoted to a web element that does not contribute to the finished appearance of the completed printing job. However, such tractor pin feed strips have been considered, until now, a "necessary evil" since they ensure accurate feeding and registration of web through a utilization device.
It is, therefore, an object of this invention to provide a reliable system for feeding continuous web through a utilization device that does not entail the use of wasteful edgewise strips having tractor pin feed holes.
It is another object of this invention to provide a system and method for feeding web that ensures accurate registration of the web with other moving elements of a utilization device and enables web to be directed to a variety of locations.